The methods of making colored glass include an ion-exchange method wherein inorganic salts of silver or copper are applied onto a glass surface and calcined, so that the ultrafine particles of the inorganic salt of silver or copper are allowed to penetrate into the glass substrate, thereby causing a transparent colloidal color development, and a method wherein a metallic film is vacuum deposited on a glass substrate by use of sputtering techniques. Moreover, there is a method wherein an oxidant of a metal salt is dissolved in a metal alkoxide solution and applied onto a substrate, followed by thermal treatment to form a film of ultrafine particles of the metal.
Especially, the color development caused by the surface plasmon of the ultrafine particles of a metal has been heretofore utilized in coloration of ceramic wares because of the good heat resistance and weatherability. For instance, in accordance with J. Sol-Gel Sci. Techn. 1, 305-312 (1994), a colored film is obtained by coating an alkoxide solution of chloroauric acid and a silane on a glass substrate, and thermally treating the coating to form ultrafine particles of gold. Further, according to the invention described in Japanese Laid-open Patent Application No. 6-191896, fine particles of gold are deposited on a glass substrate by thermal decomposition to obtain a colored film composed, for example, of gold fine particles-titanium oxide-silica, with the reflectance being as excessively high as 11.7% at minimum.
On the other hand, those glasses for vehicles or buildings which have a colored film adhered thereto, such as by coating, usually exhibit a high reflectance at the glass surface, and there are known few colored film-attached glass articles of low reflectance. If the reflectance at the glass surface is high, drivers of cars running on the opposite lane become dazed, constituting a hindrance to their driving. In contrast, the glass surface of a low reflectance makes a very calm impression.